Interesting, thank you for your experiences. Unfortunately I fly USA registered aircraft and my company has been fined/penalized for not successfully making a call ahead to PRC in the past. I'm not sure which airway/FIR the problems occurred in, but of course now they are very emphatic about making sure we do it if the chart indicates the requirement.
I suppose all I can do if they won't answer is try 6 or 7 published frequencies and broadcast in the blind if no answer, to at least say we tried, similar to Kolkota on A599.